It is known that the surfaces of implanted medical devices, in direct contact with blood, must in no way impair blood tissue, nor stem the flow of blood. They must therefore be perfectly hemocompatible.
Moreover, it is known that expanded polytetrafluoroethylene, generally denoted in the art by e-PTFE, is widely used for producing such hemocompatible articles (see, for example, the documents U.S. Pat. No. 4,743,480, WO-95/05277, WO-96/00103, U.S. Pat. No. 5,665,114, EP-0 692 264, U.S. Pat. No. 6,039,755, WO-02/100454 and WO-03/093356). The reason for this is that e-PTFE has remarkable hemocompatibility properties, especially as regards chemical stability and porosity. However, its high degree of crystallinity (close to 95%) and its unique three-dimensional structure consisting of nodes and fibers give it a high shape memory, even at high temperature.
Therefore, the hemocompatible articles made of e-PTFE that can be obtained at the present time necessarily have simple shapes, such as sheets or tubes.